This invention relates to the regeneration of molten zinc halide catalysts used in hydrocracking predominantly polynuclear aromatic hydrocarbonaceous materials; and, more particularly, in the conversion to gasoline of substantially non-distillable, high molecular weight, predominantly polynuclear aromatic hydrocarbonaceous feedstocks which contain nitrogen, oxygen and sulfur compounds. Examples of such feedstocks are coaly solids and pyrolytic products derived from coal solids such as coal extracts.
A process for utilizing molten zinc halide in such catalytic hydrocracking is described in British Pat. No. 1,095,851. As set forth in that patent, it was found that polynuclear hydrocarbons, even those which are non-distillable, may be readily converted in the presence of a large quantity of molten zinc halide to low boiling liquids suitable for fuels such as gasoline. The amount of zinc halide which serves as catalyst must be at least 15 weight percent of the inventory of hydrocarbonaceous material in the hydrocracking zone. To this amount of zinc halide must be added, in the case of nitrogen- and sulfur-containing feedstock, sufficient zinc halide to remove reactive nitrogen and sulfur compounds in the feedstock, in accordance with the following equations in the case of zinc chloride: EQU ZnCl.sub.2 + H.sub.2 S = ZnS + HCl (1) EQU ZnCl.sub.2 + NH.sub.3 = ZnCl.sub.2.NH.sub.3 ( 2) EQU znCl.sub.2.NH.sub.3 + HCl = ZnCl.sub.2.NH.sub.4 Cl (3)
In the case of a feedstock consisting of coal extract containing, for example, 1.5 percent N and 2 percent S, the amount of zinc chloride required to react stoichiometrically with the nitrogen and sulfur compounds would be 23 percent by weight of the feedstock.
Again, using zinc chloride as illustrative of the zinc halides, the spent zinc chloride melt from the hydrocracking zone contains (in addition to zinc chloride) zinc sulfide (see Equation 1), ZnCl.sub.2.NH.sub.3 (see Equation 2), organic residue, and generally ash, as well as zinc oxide if the latter were used as an HCl acceptor. U.S. Pat. No. 3,355,376 describes two methods of regenerating the spent zinc halide melt, both involving oxidation of the impurities, one in liquid phase and one in vapor phase. The reactions occurring in such oxidative regenerative processes in the case of zinc chloride are set forth in the following equations: EQU NH.sub.3 + 3/4 O.sub.2 = 1/2 N.sub.2 + 3/2 H.sub.2 O (4) EQU znO + 2 HCl = ZnCl.sub.2 + H.sub.2 O (5) EQU znS + 3/2 O.sub.2 = ZnO + SO.sub.2 ( 6) EQU c + o.sub.2 = co.sub.2 ( 7) EQU c + 1/2 o.sub.2 = co (8)
in vapor phase oxidation, air is used to effect combustion of the organic residue, to thereby establish and maintain a temperature in the regenerator at which zinc chloride is vaporized. The effluent zinc chloride vapors carry with them zinc values in the form of "free" zinc oxide and zinc oxide chemically combined with acidic oxides such as silica found in the ash of coaly solids.
The primary object of the present invention is to provide a process for regenerating spent zinc halide in which the loss of zinc values in a vapor phase oxidative regenerative process is minimized.
The following patents were considered in the preparation of this application:
Br. Pat. No. 1,095,851 PA1 U.s. pat. No. 3,355,376 PA1 U.s. pat. No. 3,371,049 PA1 U.s. pat. No. 3,594,329 PA1 U.s. pat. No. 3,625,861 PA1 U.s. pat. No. 3,629,159